The present invention relates to a pneumatic tire which improves attenuation properties without deteriorating cut resistance and weathering in a side portion thereof.
In pneumatic tires, particularly pneumatic tires for a competition such as a rally tire, which is used for a car running on a rough road such as a wasteland, a tire stiffness has been increased with an improvement of a car performance and an increase of a weight of the car.
Nevertheless, as the tire stiffness is increased, it becomes more difficult to attenuate impact applied to the tire from the ground at the time of rotations of the tire. Thus, this leads to a disadvantage that the tire vibrates, and ground contact properties, braking ability and driving stability are deteriorated.
Accordingly, although cut resistance and weathering can be improved by increasing the tire stiffness in a side portion thereof, it is practically impossible to improve attenuation properties.
The object of the present invention is to provide a pneumatic tire which is capable of improving attenuation properties without deteriorating cut resistance and weathering in a side portion thereof. By improving the attenuation properties, ground contact properties, braking ability and driving stability and the like are improved.
To achieve the above described object, in a pneumatic tire in which a carcass layer is provided in each of a pair of bead portions and a plurality of belt layers are arranged outside the carcass layer corresponding to a tread, the tire is loaded on a standard rim, a vertical distance from an end in a tire width direction in a region where a first belt layer among the belt layers disposed closest to the carcass layer and the carcass layer contact to each other to a position of a bead core center of the bead portion is set to H when internal pressure of 10% of the maximum air pressure is charged. A side portion occupying a region of 55 to 100% of H from the bead core center Q of the bead portion is constituted by an inner layer made of a compound showing tan xcex4(20xc2x0 C.) 0.25 to 1.00, disposed on the outside of the carcass layer, and an outer layer made of a compound showing tan xcex4(20xc2x0 C.) 0.15 to 0.20, disposed on the outside of the inner layer.
As described above, since the side portion is constituted by the inner layer and the outer layer, the above-described object can be achieved. Here, the standard rim and the maximum air pressure means the ones according to JATMA standard on 1999. xe2x80x9ctan xcex4(20xc2x0 C.)xe2x80x9d is measured under conditions of temperature of 20xc2x0 C., an initial strain of 10%, an amplitude of xc2x12% and a frequency of 20 Hz using a visco-elastic spectrometer. The compound means a rubber composition obtained by blending compounding agents such as sulfur and carbon black into rubber such as natural rubber, styrene-butadiene copolymer rubber and butadiene rubber according to demand.